Resilient yoke mounting for vibratory pile driver and extractor



March-24, 1970 A. E. HERZ 3,502,160

RESILIENT YUKE MOUNTING FOR VlbRATORY FILE: DRIVER AND EXTRACTOR FiledDec. 16, 1968 2 Sheets-Sheet 1 INVENTOR AL V/A/ E. #542 United StatesPatent C) 3,502,160 RESILIENT YOKE MOUNTING FOR VIBRATORY PILE DRIVERAND EXTRACTOR Alvin E. Herz, Nutley, N.J., assignor to L. B. FosterCompany, Pittsburgh, Pa., a corporation of Pennsylvanla Filed Dec. 16,1968, Ser. No. 783,869 Int. Cl. E02d 7/18 US. Cl. 173-49 Claims ABSTRACTOF THE DISCLOSURE A combined vibratory pile driver and extractor has ayoke assembly connected to a hoisting cable and a body assembly attachedto a pile. The pile is subjected to vibrations generated by the rotationof eccentric weights mounted on the body. When the weight of themechanism rests on the pile, the pile is driven into the ground. Withthe cable exciting an upward pull on the yoke, a driven pile can beextracted from the ground. To prevent impacts between yoke and body whenpile driving and to suppress cable vibrations when pile extracting, theyoke is connected to the body by two separate sets of spring means. Thefirst set has a defined stiffness that is sufficient to resist theinertial tendency of the yoke to separate from the body when driving apile, but not suflicient to prevent separation of yoke and body by adistance greater than the maximum amplitude of the vibrations of thebody when extracting a pile in response to minimum upward pull of thecable on the yoke. The second set of spring means has substantiallygreater stiffness than the first set for suppressing cable vibrationswhen substantially greater upward pull of the cable is required toextract a pile.

This invention relates to a resilient yoke mounting for use with acombination vibratory pile driver and extractor of the type in whichrevolving eccentric weights create an up and down motion that is imparedto a pile, either for driving or extracting it. The mechanism includes abody assembly that can be attached to the pile and vibrated bysynchronized rotation of eccentric weights mounted on the body. To thetop of the body assembly is connected a yoke assemgly, and to that isattached a hoisting cable for manipulating the driver-extractormechanism and for applying an upward pulling force thereto forextracting a pile from the ground. The yoke and body assemblies cannotbe ridigly connected together, however, because the hoisting cable wouldthen be subjected, during pile extracting, to severe vibrations thatwould not only whip and strain the cable itself but also possibly damagethe hoisting machinery. Accordingly, it has been customary to connectthe body and yoke assemblies by resilient spring means.

Such spring means must be stiff enough to hold the yoke tightly againstthe body, or more usually against a resilient pad or cushion disposedbetween the yoke and body, during pile driving operations when theweight of the driver-extractor substantially rests on the pile and iseffective, together with the vibrations imparted to the pile, to forcethe pile into the ground. During this operation, there is a tendency forthe yoke, because of its own inertia, to move away from the body at theend of each upward vibratory movement. If the springs are not stiffenough to restrain the yoke from doing so, then yoke and body willeither bang against each other or against the resilient pad betweenthem, to the damage of the engaging parts.

On the other hand, during the extracting operation, the cable not onlysupports the entire weight of the drivervibrator but also applies anadditional upward pulling force to help extract the pile from theground. If the spring means joining yoke and body are too stiff, thenvibrations will be transmitted directly to the cable and ultimately tothe hoisting apparatus, causing undesirable wear on those elements.Moreover, if the spring means are of some intermediate stiffness thatwill permit some slight separation between yoke and body during pileextracting, but a separation that is less than the maximum amplitude ofthe vibrations, then yoke and body will again bang each other, or theresilient pad between them. In other words, when extracting piles, thespring means should not be so stiff as to prevent the upward pull of thecable from separating the yoke and body by an amount greater than themaximum amplitude of the vibrations generated by the revolving eccentricweights.

Heretofore, these seemingly irreconcilable conditions of springstiffness were met by tightening the spring means to increase theirstiffness before the beginning of each pile driving operation and byloosening them again to reduce their stiffness before the beginning ofeach extracting operation. Since there are multiple spring meansconnecting the yoke and body, considerable time is lost in adjustingthem between the different operations. In fact, the loss of time becomesintolerable when the apparatus is used in one of the applications forwhich it is otherwise most qualified, that is, in probing unknown soilconditions in which a brief period of pile extracting precedes a periodof pile extracting that is in turn followed by relocating the pile andrenewed pile driving.

-It is accordingly among the objects of the present in vention toprovide a resilient spring mounting between the yoke and body assembliesof a combined vibratory pile driver and extractor that will providesufiicient spring stiffness to prevent substantial separation of yokeand body during pile driving operations and, without requiring anyadjustment, will provide sufiicient spring resilience to permitseparation of those elements by an amount greater than the maximumamplitude of the vibrations of the driver-extractor during pileextraction operations.

Other objects of the invention will be apparent from the followingdescription of a preferred embodiment in connection with the attacheddrawings, in which FIG. 1 is a front elevation of a combined vibratorypile driver and extractor, with some parts broken away to provide afragmentary view of the resilient mounting of this invention; and

FIG. 2 is a fragmentary side elevation, partly in section, of a portionof the resilient mounting shown in FIG. 1.

Referring to the drawings, FIG. 1 shows a generally conventionalcombined pile driver and extractor, having a body assembly 1 and rigidlyattached thereto a head 2 adapted to grip the upper end of a pile (notshown) and to subject it to periodic vibrations for driving it into theground or for extracting it from the ground. On the body assembly aremounted a plurality of eccentric weights 3 which revolve in oppositedirections in phased synchronization on horizontal shafts 4 to generateresultant vibrations in an up and down direction, those in otherdirections canceling out. Motors 6 for rotating the eccentric weightsthrough suitable drives are supported in side cases 7, which arepivotally and resiliently suspended on either side of the body assembly.A spring box 8 of rectangular cross section forms the upper part of thebody assembly. An abutment member 9 is rigidly connected to the top 10of this box.

A yoke assembly 11 is resiliently supported by the spring means of thisinvention on the body abutment member 9. The lower part .of the yokeforms a spring housing that includes front and back plates 12, sideplates 13, and an abutment member 14 at the bottom of the housing.Preferably, a resilient pad 16 is disposed between the abutments 9 and14. The upper part of the yoke is provided with pin means 17, to whichis attached a cable 18 for lifting the driver-extractor and for applyingan additional upward pull thereon when extracting piles from the ground.

The yoke and body assemblies are held in vertical alignment with eachother and are resiliently interconnected by a plurality of spacedparallel rods 21 slidably extending through holes in the body and yokeabutment members 9 and 14, and in the pad 16; and by an upper set 22 ofcompression coil springs and a lower set 23 of similar springs, each setsurrounding the rods 21 and held thereon by spring guide and retainerplates 24 slidably mounted on the rods and by nuts 26 threaded on theends of the rods. By adjusting the nuts, the stiffness of both sets ofsprings can be varied within desired limits. In the embodiment shown inthe drawings, the upper springs 22 contained within the spring housingof the yoke assembly have a stiffness approximately one half that of thelower springs 23 in the spring box on the body assembly. If desired, thelocation of these sets of springs could be reversed.

The stiffness of the upper (i.e., weaker) springs 22 is such that theywill hold the abutment members 9 and 14 tightly against each other, oragainst the resilient pad 16, when driving a pile. During suchoperation, there is either no tension on the hoisting cable 18 or onlysuch slight tension as may be initially required to support thedriver-extractor and its connected pile. In other words, the onlysubstantial force tending to separate the yoke and body assemblies underpile driving conditions is the upward force resulting from the inertiaof the yoke assembly, which tends to continue moving upwardly at the endof each upward cycle of vibration and thereby to move away from the bodyassembly that is positively urged downwardly by the inertial impulses ofthe re-, volving eccentric weights. It is this separating force that theupper set of springs 22 is designed to overcome. Because of the muchgreater stillness of lower springs 23, under the conditions just statedthe deformation of springs 23 is slight and the operative resilientconnection between the yoke and body assemblies is substantially limitedto the upper springs 22.

Springs 22 are soft enough, however, to assure that the normal minimalupward pull of the cable required for extracting piles from the groundwill separate the yoke and body abutments from each other, or one ofthem from the resilient pad 16, by an amount greater than the maximumamplitude of the vibrations imparted to the body assembly by therotating weights. Such normal minimal upward pull will, of course, varywith soil conditions, the shape and size of the pile, and the depth towhich the pile was previously driven. A broad range of such variablescan be accommodated by the occasional tightening or loosening of nuts 26on the ends of the rods to adjust the stiffness of both sets of springs.

Since an even greater upward pull may be exerted by the cable under lessfavorable conditions of pile extraction, means are provided forpositively limiting the compression of the upper spring means 22 and fortransferring the larger pulling'forces of the cable to the stiller lowerset of springs 23 housed in the body assembly. Such means for limitingthe compression of the upper springs 22 may include cylindrical skirts31 welded to the underside of the upper spring plate 24 and extendingdownwardly around the outer coil of each spring 22 in the upper set ofsprings (there being four springs in that set as shown in the drawings,one for each of the four rods 21). These skirts extend downwardly farenough to strike the upper surface of yoke abutment member 14 when thesprings have been compressed to the extent necessary to provide thedesired separation between the yoke and body abutment members and beforethe coils of the upper springs 22 have completely bottomed.

It is among the advantages of the present invention that a combinedvibratory pile driver and extractor, in which the yoke is resilientlyconnected to the body as herein described, can be used for alternatelydriving and extracting piles under most conditions met in actualpractice without intervening adjustments of spring stillness to assureretention of the yoke on the body during pile driving operations and theadequate separation of those elements during pile extracting operations.As a result, the potentialities of this type of equipment can be morefully realized, without the inconvenience, delay, and expense ofreadjusting the spring stillness with each and every change inoperations as required by conventional yoke mountings.

What is claimed is:

1. In a combined vibratory pile driver and extractor that includes abody assembly the lower part of which is adapted to be connected to theupper end of a pile and to subject the pile to vibrations generated byrotating eccentric weights on the body and the upper part of which isprovided with a first abutment member, and that also includes a yokeassembly the upper part of which is adapted to be attached to a hoistingcable and the lower part of which is provided with a second abutmentmember, the improvement comprising means for resiliently interconnectingthe two abutment members to reduce substantially impacting engagementsbetween them and to suppress or reduce vibrations transmitted to thecable, said means including: a plurality of spaced parallel rodsslidably passing through both abutment members, retaining means on theends of each rod, first spring means resiliently spacing one end of eachrod from one of the abutment members and second spring means resilientlyspacing the other end of each rod from the other abutment member, thefirst spring means having a defined stiffness substantially less thanthat of the second spring means, such stiffness being suflicient toprevent substantial inertial separation of the two abutment members whenthe vibratory mechanism is driving a pile but not suflicient to preventseparation of the two abutment members by a distance greater than themaximum amplitude of said vibrations when the vibratory mechanism isextracting a pile in response to an upward pull exerted on the yoke bythe cable.

2. Apparatus according to claim 1 that also includes a pad of resilientmaterial between the two abutment members.

3. Apparatus according to claim 1, in which the retaining means on atleast one end of each rod includes means threadably received thereon foradjusting the stiffness of the retained spring means.

4. Apparatus according to claim 1 that also includes means forpositively limiting the deformation of the first spring means to apredetermined load and for transferring loads in excess of that amountto the second spring means.

5. Apparatus according to claim 4, in which said limiting means includerigid spacer elements disposed parallel to the axes of the spring means.

References Cited UNITED STATES PATENTS ERNEST R. PURSER, PrimaryExaminer U.S. Cl. X,R, 1739 1

